of the FisJtery Board for Scotland. 265 



Metapterygoid (m. Pt.). 

 Cod, Fig. 38, PI. X. : Saitiie, Fig. 15, PL X. : Lythe, Fig. 11, PI IV. 



The metapterygoid is a generally triangular bone, with a slender apex, 

 which is superior. In the upper part of this bone there is in the cod a 

 flat plate standing almost perpendicular to the rest of the bone. It begins 

 about the middle of the bone and rises to its greatest height just before 

 reaching the level of the apex. This flat expansion is, when the bone is 

 viewed edgeways, triangular, and very broad superiorly. It forms the 

 part which unites with the anterior surface of the first process of the 

 hyomandibular, which, as was noted above, is very broad in the cod. In 

 the lythe this ridge of the metapterygoid is very narrow. In the saithe, 

 instead of a ridge running vertical to the plane of the bone, as in the cod, 

 there is a wing-like expansion broader than the ridge in the lythe, and 

 much narrower than that of the cod ; it rises at an angle from the edge of 

 the bone, and is continued superiorly to give a broad apex to the same. 



The metapterygoid is united by sutures with the pterygoid, syraplectic, 

 and hyomandibular ; it is bound to the quadrate by cartilage. 



Symplectic (Sy.). 



Cod, Fig. 39, PI. X.: Saithe, Fig. 17, PL X.: Lythe, Fig. 11, PL IV. 



A large portion of the symplectic lies in a groove on the inner 

 surface of the quadrate. In the case of the cod nearly all the lower half 

 of the bone is thus enclosed, while in the lythe a little less than the half, 

 and in the saithe only the lowest third take part in the articulation witli 

 the quadrate. On the posterior edge of the symplectic, just where it 

 leaves the quadrate, there is in the saithe a hook-like expansion. In the 

 lythe there is an angle, but not a backward-turned process as in the saithe. 

 In the cod there is a downward expansion of the internal surface of the 

 bone to form a broader area for articulation with the quadrate. 



Quadrate (Q.). 

 Cod, Fig. 44, PL X. : Saithe, Fig. 16, PL X. : Lythe, Fig. 11, PL IV. 



The quadrate is united with the symplectic and lower part of the pre- 

 operculum behind and with the pterygoid in front ; above, it is bound 

 to the metapterygoid by cartilage. 



The main point of difference between the bones of the three species is 

 in the comparative breadth of the broad articular plate which serves for 

 attachment of the cartilage uniting it with a similar part of the 

 metapterygoid. In the saithe and lythe this articular plate constitutes 

 the greater part of the superior portion of the bone. In the cod, however 

 it is seen in external view to occupy less than half of that region. This 

 is due to the fact that a part of the articular area is hidden by the forward 

 growth over it of the bone in the region of the groove which serves for 

 articulation with the syni[»lectic. 



The hind process of the quadrate which unites with the lower part of 

 the preoperculum is longer and stouter in the saithe than in the lythe, 

 and the articular groove in its posterior surface is deeper than in the latter. 

 The groove, moreover, twists outwards and backwards considerably, while 

 in the lythe the torsion if present is slight. 



